1. Field of the Invention
The present invention relates to precision sower operable to deposit individual seeds in the ground at regular intervals along a drill line.
Precision sowers are know to be employed specifically for the cultivation of corn, sugar beets, soya beans, vegetables, and in general for the cultivation of any crop whose seeds, nude or encapsulated, must be deposited at regular intervals. In comparison to the universal type of sowers, precision sowers offer various advantages: a reduction or even elimination of the time otherwise required for the thinning out of the seedlings, simplification of the cultivation and harvest operations, and considerable savings of seeds to be dispensed.
Precision sowers are substantially divided into two categories on the basis of the dispensing system employed, namely, a mechanic and a pneumatic system.
The present invention is directed to precision sowers of the pneumatic type in which the extraction of the seeds from a supply container, their separation and their individual release are accomplished by means of a rotating disc which is provided with one or more concentric circular rows of perforations, a suction fan creating a vacuum through the perforations of the disc effective to retain the seeds on the disc, and a mechanical stripper stripping surplus seeds from the disc to return the seeds to the supply container to thereby ensure the discharge of individual seeds.
2. Description of the Related Art
With known precision sowers in which the perforations of the disc are substantially circular, it is difficult to achieve the retention of only one seed at each perforation of the disc, particularly when the seeds are irregularly shaped. For this reason there is a tendency to employ a disc with oversized perforations to thereby ensure the retention of at least one seed at each perforation. Although the size of the perforations is effective to ensure the retention of even large seeds, comparatively small seeds may pass through the perforations or a number of small seeds may become so jammed in a perforation as to obturate it. It is difficult to strip such surplus seeds from the disc while leaving only a single seed at each perforation, and seeds jammed in a perforation may be damaged by the stripper cooperating with the perforated disc. To relieve these problems, it is customary to provide the sower with a number of interchangeable discs having perforations of different sizes for adaptation to seeds of different shapes and average sizes.
In addition, the stripper has to be positionable and adjustable so as to ensure the retention of only a single seed at each perforation. In known sowers this feat is impossible to accomplish in the case of irregularly shaped seeds because an adjustment which permits the separation of two smaller seeds at a single perforation may frequently lead to a larger seed being stripped off the disc, resulting in a gap in the drill line. On the other hand, an adjustment of the stripper ensuring the retention on the disc of larger or incorrectly positioned grains would permit more than one seed of a smaller size to be retained at a single perforation, resulting in an irregular seed distribution.
Italian Patent No. 1,145,917 discloses a precision sower of the pneumatic type in which the seeding disc comprises two parts, namely, a disc body connected to the suction fan, and a disc sheet contacting and covering the disc body on its side facing the seed supply. The disc body is stationary and provided with a spiral guide groove extending from its center to its outer periphery to define a seed ejection path. The disc sheet is rotatable and provided with a plurality of radial grooves extending from a center location to the periphery of the disc. With this structure, seeds may be withdrawn from the supply container at a slower speed to thereby facilitate the retention of the seeds on the disc. On the other hand, the radial grooves have to be adequately spaced for permitting the seeds to adhere to the disc at a relatively small central area thereof, whereby the number of these grooves is limited. As a result, only a small number of seeds is dispensed during each revolution of the disc, whereby the sowing operation has to be carried out at a very slow speed of advance. If the sowing operation were carried out more quickly, the seeds would be subjected to excessive centrifugal forces. This system functions well with round seeds but is less satisfactory for dispensing irregularly shaped seeds, for instance elongate seeds or seeds having varying dimensions.
In addition, this dispenser is structurally complex as it requires a disc of two parts each provided with particular slots and grooves. From a functional point of view, as the seeds come into contact with both parts of the disc, they are forced to undergo a rolling motion which, although promoting the separation of the seeds, may result in their being damaged by their frictional contact with the surfaces of the two parts of the disc over a considerable distance.
European Patent Application EP-A-0 338 883 discloses a precision sower of the pneumatic type in which the dispenser disc is provided with equidistant circular perforations disposed along one or two circular rows adjacent the outer periphery of the disc. A characteristic of the dispenser of this sower is that the vacuum system includes an internal passage having a varying cross section and divided into two branches, one of which is provided with a closure element operable to isolate it from the suction fan. In one embodiment, the dispenser disc is provided with circular perforations disposed along two circular rows, and a series of blades alternating with the perforations and acting to agitate the seeds in the container and to convey them from the point whereat the vacuum retention terminates to the point whereat the seeds are dropped to the ground. In this embodiment, as the seeds pass from one of the circular rows of perforations to the other, the individual seeds separate from one another independently, within certain limits, of the size and the shape of the seeds. On the other hand, it is evident that the space occupied by the blades between adjacent perforations limits the number of perforations which can be provided in each circular row, and thus also the number of seeds that can be dispensed during each revolution of the disc. This again implies that the speed of advance in the field is limited in order to prevent an excessively high rotational speed of the disc with its negative effects on the seeds due to centrifugal forces. Finally, this system is rather expensive.
In a second embodiment, similar to conventional pneumatic precision sowers, the disc is not provided with blades. Rather, a stripper which has rectilinear incisions and is adjustable in position relative to the perforations of the disc is provided so that the seeds retained on the disc by the vacuum strike the projections of the stripper and are thus separated into individual seeds. In any case, the dispenser of this sower also offers merely limited advantages. The circular perforations of the dispenser disc may, on the other hand, not have a diameter large enough to prevent seeds from becoming jammed therein or from passing therethrough, nor may they, on the other hand, have a small diameter because in this case the vacuum might be insufficient for withdrawing the seeds from the supply hopper. In addition, the efficiency of the stripper is unsatisfactory in the case of seeds having irregular shapes and sizes.
Similar sowers are disclosed in FR-A-2 643 212, GB-A-2 132 395, U.S. Pat. No. 3,990,606 and U.S. Pat. No. 4,074,830.
European Patent Application EP-A-0 536 543 of the present Applicant discloses a pneumatic precision sower having a dispenser disc provided with perforations and cooperating with a seed supply container and an air aspiration system. The perforations of the disc are elongate. A stripper cooperates with the disc by overlying areas of the perforations. This dispenser solves to a substantial degree the problems of the above-described state of the art sowers but does not fully eliminate the problem relating to elongate, very narrow seeds (for instance, certain hybrid corn seeds, sunflower seeds and the like) which may still get caught in or pass through the perforations of the dispenser disc.